Display document views (#849)

* Display who has viewed a document in the header

* Add overflow, display of WHEN last viewed
Cleanup old document attributes
Add firstViewedAt, lastViewedAt to API response

* Cleanup

* Added: API documentation for views endpoints

* Include views for deleted users

app/models/View.js

@@ -0,0 +1,14 @@
+// @flow
+import BaseModel from './BaseModel';
+import User from './User';
+
+class View extends BaseModel {
+  id: string;
+  documentId: string;
+  firstViewedAt: string;
+  lastViewedAt: string;
+  count: number;
+  user: User;
+}
+
+export default View;